1. Field of Invention
The invention relates to a method for copy protection of digital content according to claim 1, to a storing medium comprising digital content being copy protected according to the method and to a reproducing apparatus for executing the steps of the method.
2. Description of the Related Art
Digital technology not only allows to digitise contents, such as still images, audio and films, but also to make perfect copies of contents, once it is digitised. Digital contents can be copied perfectly, allowing an unlimited number of copy generations. While this is convenient for content consumers, it poses various problems for content producers and results in an extraordinary monetary damage both for the owner of the respective intellectual property and for the resellers and support providers.
Therefore, the providers of digital data are searching for solutions to prevent manufacture and distribution of illegally copied digital data.
Most of the prior art addresses the problem of copying by transforming the digital contents into an illegible form, e.g. by scrambling or encrypting it using cryptographic techniques. Consumption of content is now only possible with additional knowledge and/or techniques, e.g. a decryption key or an unscrambling algorithm. Merely copying contents is still possible, but no longer sufficient for the consumption of the contents. Such methods are commonly referred to as digital right management (DRM).
Replaying DRM protected contents on computers usually requires installation of appropriate DRM software. This, however, may be problematic when legitimate owners of digital contents want to move their collections of contents, and with it the necessary DRM system components to a new location, e.g. a newly bought computer or from home to the car stereo system or the like. Another problem of current DRM technology are threads from so-called system level attacks: to ensure compatibility of a given DRM enabled player with all contents available for it, all instances of this player are essentially identical. Breaking one instance potentially comprises all instances, i.e. the whole system. Further, DRM employ copy protection methods such as passwords, keywords or licences, which have to be input by the user whenever consuming some contents, which is not user-friendly.
A first step towards solving the above problems is the use of active contents, where contents are merged with the methods for its protection. Active contents comprise a passive part, which is digital content such as still image, audio track, a video sequence, text content or the like and an active part, providing DRM methods for the protection of the passive part. As common in the prior art, the passive part is transformed by the content provider and to an illegible form, e.g. by encryption. The active part is some form of executable code, capable of inverse transforming the passive part and thus making it available for consumption. The active part also implements methods governing the usage of the contents contained in the passive part, such as replay and copying. That way it reflects the usage rules devised by the content provider.
A problem of the above described active content is, that active content on its own cannot decide for a given copy whether it is an original or a copy. Active contents can be copied perfectly, just as ordinary digital contents can. Executing the original and the copy of a fully self-contained active content necessarily leads to the exact same result, which would foil any DRM effort. Active content therefore needs some form of external information with which it can upon instantiation recognise its environment and/or retrieve its previous instantiation state.
It is therefore an object of the present invention to provide a method for copy protection of digital content, which highly discourages illegal copying of digital content and which is independent from DRM systems and therefore very user-friendly as the user does not have to administrate keywords, passwords or licences required for DRM systems.
This object is achieved by a method as defined in claim 1.